1. Field of the Invention
The present invention relates to an X-ray detector, and more particularly to an X-ray detecting device and a fabricating method thereof that is capable of preventing breakage of a transparent electrode.
2. Discussion of the Related Art
Generally, an X-ray imaging system for photographing an object using a non-visible light ray such as an X-ray, etc. has been used for medical, science and industry applications. This X-ray imaging system includes an X-ray detecting panel for detecting an X-ray passing through an object to convert the X-ray into an electrical signal.
As shown in FIG. 1, the X-ray detecting panel includes a photo sensitive layer 6 for detecting an X-ray, and a thin film transistor array 4 provided on a substrate 2 to switch and output the detected X-ray signal from the photo sensitive layer 6. The thin film transistor array 4 includes pixel electrodes 5 arranged in a pixel unit, and thin film transistors (TFT's), each of which is connected to a charging capacitor Cst, a gate line 3 and a data line (not shown). On the upper portion of the photo-sensitive layer 6 is provided a dielectric layer 7 and an upper electrode 8, which is connected to a high voltage generator 9. The photo-sensitive layer 6 made from a selenium with a thickness of hundreds of micrometers μm detects an incident X-ray to convert it into an electrical signal. In other words, the photo-sensitive layer 6 produces an electron-hole pair when an X-ray is incident thereto and separates the electron-hole pair when a high voltage of several kV generated from the high voltage generator 9 is applied to the upper electrode 8. Holes separated from electrons are charged in the charging capacitor Cst by way of the pixel electrode 5, and a portion of the holes is accumulated on the surface of the pixel electrode 5. This results in the number of holes accumulated in the charging capacitor Cst being reduced. In order to prevent such a reduction, a charge blocking layer 11 is formed on the pixel electrode 5. The thin film transistor (TFT) responds to a gate signal inputted over the gate line 3 to apply a voltage charged in the charging capacitor Cst to the data line. Pixel signals supplied to the data line are applied to a display device via a data reproducer, thereby displaying a picture.
FIG. 2 is a cross-sectional view showing a structure of a conventional X-ray detecting device and illustrates a thin film transistor part and a storage capacitor part.
Referring to FIG. 2, the substrate 2 of the X-ray detecting device is provided with a gate electrode 12, a semiconductor layer 34 formed with having the gate electrode and a gate insulating film 32 therebetween, a source electrode 14 and a drain electrode 16 separately formed on the semiconductor layer 34. In order to protect such a thin film transistor part, a storage insulating film 38 and first and second protective films 40 and 36 are provided. A first drain contact hole 15a passing through the storage insulating film 38 and the first protective film 40 are provided on the storage insulating film 38 and the first protective film 40, whereas a second drain contact hole 15b passing through the second protective films 36 is provided. The drain electrode 16 electrically contacts a transparent drain electrode 27 provided on the first protective film 40 via the first drain contact hole 15a. Further, the transparent drain electrode 27 electrically contacts the pixel electrode 5 provided on the second protective film 36 via the second contact hole 15b. Thus, the drain electrode 16 is in electrical contact with the pixel electrode 5 via the first and second contact holes 15a and 15b. 
The charge capacitor part Cst consists of a storage electrode 25, and the pixel electrode 5 positioned over the storage electrode 25 with the second protective film 36 therebetween. A ground line 22 for resetting residual charges of the charging capacitor Cst contacts the lower portion of the storage electrode 25. The ground line 22 and the storage electrode 25 are in electrical contact with each other via a storage contact hole 17 through the storage insulating film 38 and the first protective film 40.
FIG. 3A to FIG. 3G are section views showing a method of fabricating the X-ray detecting device shown in FIG. 2, and illustrate the thin film transistor part and the storage capacitor part.
First, the gate electrode 12 is formed by sequentially depositing first and second gate metals 12a and 12b onto the substrate 2 and then patterning them as shown in FIG. 3A.
As shown in FIG. 3B, the gate insulating film 32, an active layer 34a and an ohmic contact layer 34b are formed by depositing an insulating material and first and second semiconductor materials onto the entire surface of the substrate 2 provided with the gate electrode 12 and then patterning the first and second semiconductor materials.
After formation of a semiconductor layer 34, as shown in FIG. 3C, the source 14, the drain electrode 16 and the ground line 22 are formed by depositing a data metal onto the gate insulating film 32 and patterning it as shown in FIG. 3C. The storage insulating film 38 and the first protective film 40 are formed by depositing first and second insulating materials on the substrate 2 provided with the source electrode 14, the drain electrode 16 and the ground line 22. The first drain contact hole 15a and the storage contact hole 17 are defined by patterning the storage insulating film 38 and the first protective film 40 as shown in FIG. 3D.
Subsequently, as shown in FIG. 3E, a transparent drain electrode 27 and a storage electrode 25 in contact with the drain electrode 16 and the ground line 22 are formed by depositing a transparent conductive material on the first protective film 40 and then patterning it.
As shown in FIG. 3F, the second protective film 36 and the second drain contact hole 15b are formed by depositing an insulating material onto the first protective film 40 and patterning it in such a manner to cover the transparent drain electrode 27 and the storage electrode 25.
Finally, as shown in FIG. 3G, the pixel electrode 5 electrically connected to the transparent drain electrode 27 via the second drain contact hole 15b is formed by depositing a transparent conductive material onto the second protective film 36 and then patterning it.
The first drain contact hole 15a and the storage contact hole 17 of the conventional X-ray detecting device are formed by simultaneously patterning the storage insulating film 38 and the first protective film 40 using a dry etching technique. In this case, the storage insulating film 38 and the first protective film 40 are formed from an inorganic insulating material and an organic material having a different etching rate, respectively. This forces an etching rate of the storage insulating film 38 to be faster than that of the first protective film 40 to over-etch the storage insulating film 38 in comparison to the first protective film 40, thereby causing an undercut phenomenon. This undercut phenomenon allows the transparent conductive material deposited on the first protective film 40 to have a poor step coverage, thereby causing a problem of a breakage of the transparent drain electrode 27 and the storage electrode 25.